1. Field of the Invention
The present invention relates to a dry-sump lubrication type four-stroke cycle engine suitable for a vehicle, such as a straddle type all-terrain four-wheel vehicle or a motorcycle, and, more specifically to improvements in an oil reserving and circulating system of the engine.
2. Description of the Related Art
A conventional dry-sump lubrication four-stroke cycle engine usually has an oil tank separated from a crank case of the engine, an oil feed pump and an oil return pump, i.e., a scavenging pump. The oil tank holds a predetermined quantity of an engine oil. The oil feed pump pumps up oil from the oil tank and feeds the oil by pressure to parts needing lubrication of the engine, and the scavenging pump pumps up used oil collected in the bottom of the crankcase or an oil pan and returns the used oil into the oil tank. This dry-sump lubrication system increases the weight, component parts and cost of the engine, and needs pipes for connecting the crankcase and the oil tank.
A dry-sump lubrication type four-stroke cycle engine previously proposed by the applicant of the present patent application in JP-A No. 288466/1994 is not provided with any external oil tank and has a transmission chamber having a lower part serving as an oil reservoir chamber. FIGS. 12 and 13 are side elevations respectively showing the left side surface of a right half-crankcase, and the right side surface of a left half-crankcase of the dry-sump lubrication type four-stroke cycle engine disclosed in JP-A No. 288466/1994.
Referring to FIG. 12, a partition wall 123 of a predetermined height is formed between a crankshaft chamber 121 and a transmission chamber 122 in a crankcase 120 to use a lower part of the transmission chamber 122 as an oil reservoir chamber 125. A triangular oil collecting chamber 126 extending rearward is formed in a lower rear part of the crankshaft chamber 121, a suction opening 127 is formed in a wall defining an axial end of the oil collecting chamber 126. A scavenging pump of the engine sucks oil dripped in the crankshaft chamber 121 and collected in the oil collecting chamber 126 through the suction opening 127 and discharges the oil into the transmission chamber 122 to keep the crankshaft chamber 121 in a dry state.
Referring to FIG. 13, a connecting hole 131 is formed in a part, in front of the oil collecting chamber 126, of the left half-crankcase to connect the bottom of the crankshaft chamber 121 and the bottom of a generator chamber (not shown) extending into the paper in FIG. 13 to let oil dripped into the generator chamber flow through the connecting hole 131 into the crankshaft chamber 121. Oil flowed into the crankshaft chamber 121 is sucked up together with oil collected in the oil collecting chamber 126 by the scavenging pump through the suction opening 127.
An engine disclosed in JP-A No. 215411/1986 has a transmission chamber having a lower part serving as an oil reservoir chamber. Although this engine is similar to that disclosed in JP-A No. 288466/1994 in forming a partition wall between a transmission chamber and a crankshaft chamber and using a lower part of the transmission chamber as an oil reservoir chamber, a generator chamber formed on one side of the crankshaft chamber and a clutch chamber formed on the other side of the crankshaft chamber are connected by a connecting passage extending under the crankshaft chamber, and the crankshaft chamber and the generator chamber are connected by a connecting hole. Oil dripped into the crankshaft chamber flows into the generator chamber, oil is contained in both the generator chamber and the clutch chamber at the same oil level, and then a scavenging pump of the engine pumps up the thus collected oil and discharges oil into the oil reservoir chamber.
In the engine disclosed in JP-A No. 288466/1994, which sucks oil from the triangular oil collecting chamber 126 formed in a lower rear part of the crankshaft chamber 121 so as to extend rearward, gases and oil are forced to flow together into the oil collecting chamber 126 by the rotation of crank arms of a crank shaft contained in the crankshaft chamber 121 and therefore, oil is unable to flow smoothly through the suction opening 127 formed in one side of the oil collecting chamber 126, which affects adversely to the suction efficiency of the scavenging pump.
Since oil dripped into the generator chamber flows into the crankshaft chamber 121 and oil is forced to flow together with oil collected in the crankshaft chamber 121 into the oil collecting chamber 126, the quantity of oil contained in the crankshaft chamber 121 increases temporarily before oil flows into the oil collecting chamber 126, which is undesirable in view of keeping the crankshaft chamber 121 of the dry-sump lubrication type engine in a dry state.
In the engine disclosed in UP-A No. 215411/1986, the generator chamber and the clutch chamber formed on the opposite sides of the crankshaft chamber communicate with each other by means of the connecting passage and hence oil remains always in the generator chamber and the clutch chamber. Consequently, a large quantity of oil flows from the generator chamber into the crankshaft chamber when the engine is tilted beyond a certain angle and hence it is possible that the crankshaft chamber cannot be maintained in a dry state.
The present invention has been made in view of the foregoing problems and it is therefore an object of the present invention to provide a compact dry-sump lubrication type four-stroke cycle engine provided with a lightweight lubricating system comprising a small number of component parts, being capable of efficiently using an oil pump, and having a large oil capacity.
According to one aspect of the present invention, a dry-sump lubrication type four-stroke cycle engine has a crankcase provided with a crankshaft chamber containing a crankshaft in its front part and a transmission chamber in its rear part, a generator chamber on one side of the crankcase in an axial direction of the crankshaft, and a clutch chamber on the other side of the crankcase; wherein the crankshaft chamber and the transmission chamber are separated by a partition wall of a predetermined height to form an oil reservoir chamber in a lower part of the transmission chamber, an auxiliary oil reservoir chamber is formed in a lower part of the clutch chamber so as to communicated with the oil reservoir chamber, a suction chamber is formed integrally with the crankcase under a crankshaft chamber bottom wall defining a bottom of the crankshaft chamber so as to communicate with a suction port of a scavenging pump of the engine, the suction chamber opens into the crankshaft chamber through a first suction hole formed in the crankshaft chamber bottom wall and opens into the generator chamber through a second suction hole formed in a wall defining a bottom of the generator chamber, and the scavenging pump pumps up oil from the suction chamber and discharges oil into the oil reservoir chamber or the auxiliary oil reservoir chamber.
According such a structure, the dry-sump lubrication type four-stroke cycle engine of the present invention is able to save external piping and mounting apace for an external oil tank, and further, is able to increase the quantity of oil that can be reserved in the crankcase without enlarging the crankcase.
Since the dead space under the wall defining the bottom of the crankshaft chamber is used as the suction chamber, the suction passage of the scavenging pump can be formed with a simple structure.
Since oil flowed from the crankshaft chamber into the suction chamber is sucked by the scavenging pump, the flow of oil into the scavenging pump is hardly affected and disturbed directly by the revolution of the crank shaft, oil can be smoothly sucked by the scavenging pump.
Since the generator chamber is connected directly to the suction chamber formed under the wall defining the crankshaft chamber by the second suction hole, suction of oil from the generator chamber is affected scarcely by pressure variation in the crankshaft chamber.
Preferably, the first suction hole formed in the crankshaft chamber bottom wall may have an elongate shape extending along an axis of a crankshaft and has a length substantially corresponding to an overall width, along the axis of the crankshaft, of crank arms of the crankshaft contained in the crankshaft chamber.
The elongate suction hole enables quick suction of oil from the crankshaft chamber.
Preferably, the scavenging pump may be disposed in the generator chamber.
Thus, oil collected in the generator chamber can be sucked through a short suction passage by the scavenging pump, which prevents the reduction of suction force that acts on oil.
Preferably, the scavenging pump may be disposed in the clutch chamber.
Thus, the scavenging pump is able to discharge oil into the clutch chamber, which simplifies discharge piping related with the scavenging pump.
Preferably, the clutch chamber and the transmission chamber may be connected by an overflow passage extending at a predetermined oil level in the oil reservoir chamber to enable oil to flow from the oil reservoir chamber to the auxiliary chamber, the clutch chamber and the suction chamber may be connected by a level limiting hole at a oil level below that of the overflow passage to enable oil to flow from the clutch chamber through the level limiting hole into the suction chamber so that oil level in the clutch chamber is maintained below that of an oil level in the transmission chamber.
Thus, even though a lower part of the clutch chamber is used as the auxiliary oil reservoir chamber, the clutch can be disposed in a lower position near the oil level, which enables forming the engine in a short height.
Preferably, respective bottoms of the clutch chamber and the transmission chamber may be connected by a connecting hole to maintain the oil level in the clutch chamber substantially equal to that in the transmission chamber.
Thus, an increased quantity of oil can be reserved in the crankcase.